1. Field of the Invention
The invention relates to a process for the production of 4,5,6,7-tetrahydrothieno-[3,2-c)-pyridines of the formula: ##STR5## wherein R is hydrogen, a formyl group, an acetyl group or a benzoyl group or is a benzyl group, which optionally is ring-substituted by at least one halogen atom. Compounds of said type have antithrombotic action by preventing blood platelet aggregation [E. Saltiel et al., Drugs, 34 (1987), p. 222].
2. Background Art
Numerous processes are known for the production of thienopyridine derivatives. Thus, a synthesis is described in West German Pat. No. 2,530,516 in the course of which bromination of an alkyl group in allyl position with N-bromosuccinimide is described. But such reactions are hardly feasible on an industrial scale.
Other production methods are described in Bull. Soc. Chim. Belgique, 79, (1979), p. 301, as well as in Arkiv Kemi., 32, (1970), pp. 217 and 249. In said reaction sequences, which take place over five or six reaction steps, acids or complex alkali metal hydrides are used. This indeed is feasible on a laboratory scale but cannot be transferred to an industrial scale. In addition, the high costs of the reagents used cause both processes to not make any economical sense. Further, the yields are very small.
Derivatives of 4,5,6,7-tetrahydrothieno-[3,2-c]-pyridine, their use in pharmaceutical agents and a process for their production have already been described in West German Pat. No. 2,404,308. In such process, compounds of the formula: ##STR6## wherein A and B each stand for at least one atom or a group of the class consisting of hydrogen atoms, halogen atoms, hydroxyl groups, lower alkyl radicals, lower alkoxy radicals, nitrogen groups and amino groups, are condensed with a halide of the formula Hal-R, in which Hal is a halogen atom and R is an optionally substituted alkyl radical, aryl radical or aralkyl radical, with formation of a pyridinium salt of the formula: ##STR7## and then such pyridinium salt is hydrogenated to the derivative of formula (1). But such process is expensive and difficult to perform, since it requires numerous and difficult process steps.